Police and Criminal Evidence Act

Police and Criminal Evidence Act 1984 Section 17
Section 17 permits a constable to enter and search any premises for the purpose of arresting a person for an arrestable offence.

Police and Criminal Evidence Act 1984 Section 18
Section 18 permits a constable to enter and search any premises occupied or controlled by a person who is under arrest for an arrestable offence if he has reasonable grounds for suspecting there is on the premises, other than items subject to legal privilege, that relates to that offence or some other arrestable offence connected with or similar to that offence.

A constable may conduct such a search before taking the person to a police station and without the written authority of an other inspector rank or above if the presence of that person at a place other than a police station is necessary for the effective investigation of that offence. The forgery and counterfeiting act 1981 section 1,2,3 and 4 and trade marks act 1994 section 92 are arrestable offences.

Police and Criminal Evidence Act 1984 Section 19
Under section 19 when a constable is lawfully on any premises he can seize anything which he finds on the premises if he has reasonable grounds for believing:

(i) that it has been obtained in consequence of the commission of an offence; or
(ii) that it is evidence in relation to an offence which he is investigating or any other offence;
And (iii) that it is necessary to seize it in order to prevent it being concealed, lost, damaged, altered or destroyed.

This also applies to information contained in a computer and he can take away hard-copy print cuts of such information. Section 20.